Immutable and unique in C#

[deadalnix]

Le 13/11/2012 08:48, Sönke Ludwig a écrit :
> Am 13.11.2012 00:46, schrieb Walter Bright:
>> On 11/9/2012 5:53 AM, Sönke Ludwig wrote:
>>> Independent of this article I think D is currently missing out a lot by
>>> omitting a proper unique type (a _proper_ library solution would be a
>>> start, but I'm not sure if that can handle all details). It would make a
>>> lot of the cases work that are currently simply not practical because of
>>> loads of casts that are necessary.
>>
>> Unique as a type qualifier comes with all kinds of subtle problems. For one thing, unique is more of
>> a property of an expression rather than a property of the type.
>>
>> But I was thinking - what if it's a storage class? Like ref is? Working through the use cases in my
>> head, I think it can work. Unique being a property of an expression, this can be tested upon
>> assignment to the unique variable. Upon reading that unique variable, the value of it is erased.
>>
>> Function parameters can be qualified with "unique" as well, meaning their corresponding arguments
>> can only be unique expressions.
>>
>
> Currently I also see no reason why this should not be possible. Since it is acting recursively and
> locally anyway, a storage class will probably capture almost everything that a full type would. I
> had thought about the same route to reduce intrusiveness, before looking first what's possible with
> a pure library solution.
>
> The library solution seems surprisingly practical for some use cases. With the concept of "string"
> and "weak" isolation (*), it can even handle the bridge between isolated and shared memory (thanks
> to the completely separated nature of shared). By this, it solves a lot of the problems that only
> Bartosz system was able to solve, for example declaring owned collections (no Mutex necessary),
> which contain references to shared data, and still everything is safely checked.
>

BTW, do you have a link to Bartosz's proposal ?

> A proper language feature can still do a lot more and IMO D should get there at some point - but I
> think this is a viable short/mid-term alternative. I would like to get some discussion going to
> eventually include something in phobos.
>
>
> (*)
>
> strong isolation: allows only strongly isolated and immutable references
>   ->  can be passed to other threads and casts implicitly to immutable
>
> weak isolation: allows weakly isolated, immutable and shared references
>   ->  can only be passed to other threads